1. Technical Field
The present invention relates to a technology for driving an electric discharge lamp which emits light by discharge generated between electrodes.
2. Related Art
A high intensity discharge lamp such as high-pressure gas discharge lamp is used as a light source of an image display apparatus such as projector. For lighting the high intensity discharge lamp, alternating current (AC ramp current) is supplied to the high intensity discharge lamp. As a method for lighting the high intensity discharge lamp by the supply of AC ramp current, such a technology has been proposed which uses AC ramp current having an approximately constant absolute value and modulated pulse width ratio of positive and negative pulse widths to be supplied to the high intensity discharge lamp so as to increase stability of light arc generated within the high intensity discharge lamp (for example, see JP-T-2004-525496).
When the high intensity discharge lamp is lighted with AC ramp current having modulated pulse width, the period for use of the high intensity discharge lamp is limited due to deterioration of electrodes or deposition (blacking) of electrode material on the interior of the high intensity discharge lamp. This problem arises not only from the high intensity discharge lamp but also from various types of discharge lamp (electric discharge lamp) which emit light by arc discharge between electrodes.